A class that uses mysql memory table to replace php session

/**
* session mysql内存表
@Usage: use some other storage method(mysql or memcache) instead of php sessoin
@author:lein
@Version:1.2
*/
session_start();
if(!isset($_SESSION['test'])){
 $_SESSION['test']="123_lein_".date("Y-m-d H:i:s");
}

class session{
    //session data
    private $data;
    //engine,mysql or memcache
    private $engine;
    //php session expire time
    private $sessionexpiredTime;
    //current user's session cookie value
    private $sessionID;
    //session coolie name
    private $sessionCookieName;
    public function session($engineBase=NULL,$engineName='mysql',$storage_name='php_session'){
        try{
            $this->sessionexpiredTime = intval(ini_get("session.cache_expire"))*10;//默认是180分钟，太长了，改为了30分钟
        }catch(Exception $Exception){
            $this->sessionexpiredTime = 1200;
        }
        try{
            $this->sessionCookieName = ini_get("session.name");
        }catch(Exception $Exception){
            $this->sessionCookieName = 'PHPSESSID';
        }

        if(!isset($_COOKIE[$this->sessionCookieName])){
            @session_start();
            $this->sessionID=session_id();
        }else{
            $this->sessionID=$_COOKIE[$this->sessionCookieName];
        }
        $className = $engineName."SessionEngine";
        $this->engine = new $className(
                                    array(
                                          'storage_name'=>$storage_name,//mysql table name or memcahce key which stores data;
                                          'expire_time'=>$this->sessionexpiredTime,
                                          'data_too_long_instead_value' => '{__DATA IS *$* TO LONG__}'
                                          ),
                                    $this->sessionID,
                                    &$engineBase
                                    );
        $this->init();
        $this->loadFromSession();
        $this->engine->refresh();
        $this->engine->cleanup();
    }
    private function init()
    {
        $this->data = $this->engine->get();
        if(empty($this->data)){
            @session_start();
            if(!empty($_SESSION)){
                $this->data = $_SESSION;
                $this->engine->create(false, $this->data);
            }
            else
            {
                $this->engine->create(false, "");
            }
        }
    }
    public function loadFromSession($flagStartSession = false){
        $flag=false;
        if($flagStartSession){
            @session_start();
        }
        if($_SESSION&&is_array($_SESSION)){
            foreach($_SESSION as $k=>$v){
                if(!isset($this->data[$k])){
                    $this->data[$k] = $v;
                    $flag=true;
                }
            }
        }
        if($flag){
            $this->engine->set(false, $this->data);
        }
    }
    private function __get($nm)
    {
        if (isset($this->data[$nm])) {
            $r = $this->data[$nm];
            return $r;
        }
        else
        {
            return NULL;
        }
    }
    private function __set($nm, $val)
    {
       $this->data[$nm] =  $val;
       $this->engine->set(false, $this->data);
    }

    private function __isset($nm)
    {
        return isset($this->data[$nm]);
    }

    private function __unset($nm)
    {
        unset($this->data[$nm]);
        $this->engine->set(false, $this->data);
    }

    function __destruct(){
        $this->data = NULL;
        $this->engine->close();
        $this->engine = NULL;
    }
}

interface SessionEngine
{
    /*
     * set varibles
     * @param $arr array,array(varible name=>varible value,...)
     */
    public function setVariable($arr);
    /*
     * get session value
     * @param $key string
     */
    public function get($key="");
    /*
     * set session value
     * @param $key string
     * @param $value string
     */
    public function set($key="",$value="");
    /*
     * set session value
     * @param $key string
     * @param $value string
     */
    public function create($key="",$value="");
    /*
     * update the session's invalid time
     * @param $key string
     */
    public function refresh($key="");
    /*
     * close mysql or memcache connection
     */
    public function close();
    /*
     * delete expired sessions
     */
    public function cleanup();
}

final class mysqlSessionEngine implements SessionEngine{
    private $id="";
    private $storage_name='php_session';
    private $storage_name_slow='php_session_slow';
    private $data_too_long_instead_value = '{__DATA IS ~ TO LONG__}';//if data is longer than $max_session_data_length and you are using mysql 4 or below,insert this value into memery table instead.
    private $expire_time=1200;
    private $max_session_data_length = 2048;
    private $conn;
    private $mysql_version;
    public function mysqlSessionEngine($arr=array(),$key="",&$_conn){
        $this->setVariable($arr);
        $this->id = $key;
        if(empty($this->id)||strlen($this->id)!=32){
            throw new Exception(__FILE__."->".__LINE__.": Session's cookie name can't be empty and it must have just 32 charactors!");
        }
        $this->conn = $_conn;
        if(!$this->conn||!is_resource($this->conn)){
            throw new Exception(__FILE__."->".__LINE__.": Need a mysql connection!");
        }
        $this->mysql_version = $this->getOne("select floor(version())");
        if($this->mysql_version            $this->max_session_data_length = 255;
        }
    }
    public function setVariable($arr){
        if(!empty($arr)&&is_array($arr)){
            foreach($arr as $k=>$v){
                $this->$k = $v;
                if($k=='storage_name'){
                    $this->storage_name_slow = $v.'_slow';
                }
            }
        }
    }
    public function get($key=""){
        if($key=="") $key = $this->id;
        $return = $this->getOne('select value from '.$this->storage_name.' where id="'.$key.'"');
        if($return==$this->data_too_long_instead_value)
        {
            $return = $this->getOne('select value from '.$this->storage_name_slow.' where id="'.$key.'"');
        }
        if(!$return)
        {
            $mysqlError = mysql_error($this->conn);
            if(strpos($mysqlError,"doesn't exist")!==false)
            {
                $this->initTable();
            }
            $return = array();
        }
        else
        {
            $return = unserialize($return);
        }
        return $return;
    }
    public function close(){
        @mysql_close($this->conn);
    }
    public function cleanup(){
        if($this->mysql_version>4){
            $sql = 'delete from '.$this->storage_name.' where date_add(`time`,INTERVAL '.$this->expire_time.' SECOND)        }else{
            $sql = 'delete from '.$this->storage_name_slow.' where `time`+'.$this->expire_time.'            if($_SESSION['username']=="leinchu"){
                echo $sql;
            }
            $this->execute($sql);
            $sql = 'delete from '.$this->storage_name.' where `time`+'.$this->expire_time.'            if($_SESSION['username']=="leinchu"){
                echo $sql;
            }
        }
        $this->execute($sql);
    }
    public function refresh($key=""){
        if($this->mysql_version>4){
            $sql = 'update '.$this->storage_name.' set `time`=CURRENT_TIMESTAMP() where id="'.$key.'"';
        }else{
            $sql = 'update '.$this->storage_name.' set `time`=unix_timestamp() where id="'.$key.'"';
        }
        $return = $this->execute($sql);
        if(!$return){
            $this->initTable();
            $return = $this->execute($sql,true);
        }
        return $return;
    }
    public function create($key="",$value=""){
        if($key=="") $key = $this->id;
        if($value != "") $value = mysql_real_escape_string(serialize($value),$this->conn);
        if(strlen($value)>$this->max_session_data_length)
        {
            if($this->mysql_version>4){
                throw new Exception(__FILE__."->".__LINE__.": Session data is long than max allow length(".$this->max_session_data_length.")!");
            }
        }
        if($this->mysql_version>4){
            $sql = 'replace into '.$this->storage_name.' set value=/''.$value.'/',id="'.$key.'",`time`=CURRENT_TIMESTAMP()';
        }else{
            $sql = 'replace into '.$this->storage_name.' set value=/''.$value.'/',id="'.$key.'",`time`=unix_timestamp()';
        }
        $return = $this->execute($sql);
        if(!$return){
            $this->initTable();
            $return = $this->execute($sql,true);
        }
        return $return;
    }
    public function set($key="",$value=""){
        if($key=="") $key = $this->id;
        if($value != "") $value = mysql_real_escape_string(serialize($value),$this->conn);
        $sql = 'update '.$this->storage_name.' set value=/''.$value.'/' where id="'.$key.'"';
        if(strlen($value)>$this->max_session_data_length)
        {
            if($this->mysql_version>4){
                throw new Exception(__FILE__."->".__LINE__.": Session data is long than max allow length(".$this->max_session_data_length.")!");
            }
            $sql = 'replace into '.$this->storage_name_slow.' set value=/''.$value.'/',id="'.$key.'",`time`=unix_timestamp()';
            $this->execute($sql,true);
            $sql = 'update '.$this->storage_name.' set value=/''.$this->data_too_long_instead_value.'/' where id="'.$key.'"';
        }
        $return = $this->execute($sql);
        if(!$return){
            $this->initTable();
            $return = $this->execute($sql,true);
        }
        return $return;
    }
    private function initTable(){
        if($this->mysql_version>4){
            $sql = "
                CREATE TABLE if not exists `".$this->storage_name."` (
                  `id` char(32) NOT NULL default 'ERR',
                  `value` VARBINARY(".$this->max_session_data_length.") NULL,
                  `time` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,
                  PRIMARY KEY  (`id`),
                  KEY `time` (`time`)
                ) ENGINE=MEMORY;
                ";
        }else{
            $sqlSlow = "
                CREATE TABLE if not exists `".$this->storage_name."_slow` (
                  `id` char(32) NOT NULL default 'ERR',
                  `value` text NULL,
                  `time` int(10) not null default '0',
                  PRIMARY KEY  (`id`),
                  KEY `time` (`time`)
                ) ENGINE=MyISAM;
                ";
            $this->execute($sqlSlow,true);

            $sql = "
                CREATE TABLE if not exists `".$this->storage_name."` (
                  `id` char(32) NOT NULL default 'ERR',
                  `value` VARCHAR(255) NULL,
                  `time` int(10) not null default '0',
                  PRIMARY KEY  (`id`),
                  KEY `time` (`time`)
                ) ENGINE=MEMORY;
                ";
        }
        return $this->execute($sql,true);
    }
    private function execute($sql,$die=false)
    {
        if($die)
        {
            mysql_query($sql,$this->conn) or die("exe Sql error:".mysql_error()."".$sql."");
        }
        else
        {
            mysql_query($sql,$this->conn);
            if(mysql_error()){
                return false;
            }else{
                return true;
            }
        }
    }
    private function getOne($sql,$die=false){
        $rs = $this->query($sql,$die);
        if($rs && ($one = mysql_fetch_row($rs)) ){
            return $one[0];
        }else{
            return false;
        }
    }
    private function query($sql,$die=false){
        if($die)
            $rs = mysql_query($sql,$this->conn) or die("query Sql error:".mysql_error()."".$sql."");
        else
            $rs = mysql_query($sql,$this->conn);
        return $rs;
    }
}
$lnk = mysql_connect('localhost', 'root', '123456')
       or die ('Not connected : ' . mysql_error());

// make foo the current db
mysql_select_db('test', $lnk) or die ('Can/'t use foo : ' . mysql_error());
$S = new session($lnk);
if(!$S->last){
 $S->last = time();
}
echo "First visit at ".$S->last."";
if(!$S->lastv){
 $S->lastv = 0;
}
$S->lastv++;
echo "lastv=".$S->lastv."";
echo "test=".$S->test."";
if(isset($_GET['max'])){
 $S->boom = str_repeat("OK",255);
}
if(isset($_GET['boom'])){
 $S->boom = $_GET['boom'];
}
echo "boom=".$S->boom."";
?>